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Study Of Adsorptive Behavior Of Analytes In SERS Analysis

Posted on:2017-04-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:P LiFull Text:PDF
GTID:1221330485453633Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
Surface-enhanced Raman Scattering (SERS) is a powerful spectral analytical technique that is based on the Raman Spectroscopy selectively recognizing biological and chemical molecules as well as providing material composition and structural information of molecules. In comparison with fluorescence approach, SERS exhibits significant advantages of resistance to photo-bleaching and photo-toxicity as well as displays narrow emission peaks for spectral multiplexing. Moreover, SERS can provide in situ on-line detection with fast response time, simple procedures and non-destructive detection. Therefore, SERS has become a powerful analytical technique and has been widely used in various fields since it integrates the advantages of providing high sensitivity and fingerprint information of molecules. Generally, the SERS activity depends essentially of four factors:(1) the electromagnetic field generated by the plasmonic nanostructure, (2) the intrinsic Raman properties of molecule (the cross-section), (3) the affinity of molecule for the plasmonic surface (adsorbent-adsorbate interaction) and (4) external condition for SERS measurement (laser, solvent, etc). In principle, all molecular systems can produce SERS activity, but not all molecules are good SERS probes. For the molecules with lower SERS activity and lower affinity with SERS substrates, SERS cannot be used to detect/recognize these species directly. As a consequence, one attempt to use indirect methods based on chemical modification and physical capturing to realize ultra-sensitive detection of various analytes. Herein, in this thesis, considering the important factors related to SERS measurement, various analytes and SERS-active substrate, we carried out the following parts:(1) We used the dynamic surface-enhance Raman Spectroscopy (D-SERS) to in situ monitor the adsorptive forms of thiram on Au NPs. D-SERS is based on state translation nanoparticles from wet state to the dry state to realize SERS detection. In the initial (wet) state, the solvent can protect the substrate and analyte from laser damage, further reducing photo-degradation problems and offering high stability. Moreover, D-SERS method can calculate the time-resolved spectra, thus based on the analysis of continuous spectra, we monitored that S-S bond of thiram molecule was broken due to possible catalysis effect of metal NPs. In addition, because of breakdown of S-S band, we also observed the different adsorptive forms of thiram at different concentrations. In short, D-SERS method can in situ continuously monitor the adsorptive forms of analytes, providing a reference and giving a help for surface science widely used in various fields.(2) SERS cannot be used to detect atomic species Hg(Ⅱ) directly, so we use the indirect approaches to realize selective and sensitive detection of Hg(Ⅱ). First, based on the electron configuration of Hg(Ⅱ), we synthesized aminated ring-close structure of R6G (R-NH2) as SERS probe for sensitively and selectively detection of Hg(Ⅱ). Because R6G-derivative exists isomers with different spectroscopic properties, namely, R-NH2 displays different molecular structure within different pH. Therefore, by using the UV-vis, Fourier-transform IR (FTIR) and SERS spectra, we analyzed stability of different structures and capability for detection of Hg(Ⅱ), further confirming the optimal condition for detection of Hg(Ⅱ). Because of the higher compound stability between R-NH2 and Hg(Ⅱ) with coordination bond and π-π conjugation than that of R-NH2 and Ag NPs, we realized the sensitive and selective detection of Hg(Ⅱ).(3) We report a surface-enhanced resonance Raman scattering (SERRS) strategy, ferric-citrate-functionalized Au nanoparticles [Au NPs/CA-Fe(Ⅲ)] sensor for detecting the release of DA in complex sample. Considering chemically modification with SERRS active improving sensitivity and selective of DA and the target of in situ collecting and carriaging DA with minimal invasion and simplification from complicated sample, we used the acupuncture needle as the promise tool. First, acupuncture needle body was decorated with 3-Mercaptopropyltriethoxysilane (3-MPTES) and then further modified with Au NPs. Moreover, using residual citrate (CA) on Au NPs as hydroxyl-carboxylic metal ligand, the further modification of Fe(Ⅲ) made the needle as SERRS active substrates Au NPs-CA-Fe(Ⅲ), easilily realizing the capture and collection of analyte with simplification and time efficiency, where Au NPs gives the necessary enhanced properties and CA-Fe(Ⅲ) acts as a molecular trap to capture and bring target DA onto Au NPs core with formation of resonant structure. Finally, we used the functionalized needle to detect DA molecules in complex samples serum and cerebrospinal fluid with sensitivity and selectivity.(4) Single hot site nanostructure was assembled for conducting dual-analyte and various analytes SERS detection. We choose the Ag NWs as template to obtain optical location during SERS measurement, Au NP as the optical antenna to couple with the surface plasmon polariton (SPP) of NW for generation of localized electromegnatic field enhancement at the junction. Firstly, the assembled method of single hot site structure is easy, and then the junction between NW and NP can provide the localized coupled plasmon. Moreover, the exact position of the single hot site can be conveniently located in situ using Raman optical microscopy, therefore, the SERS measurement is obtained by placing the laser focus onto a single Au NP-Ag NW junction, improving reproducibility and stability for measurement signals. Importantly, the self-assembled single hot site structure can form "nano-channel" with a Si wafer to capture molecules, which ensures the captured molecules are located in the hot site area. This single hot site structure not only provide reproducible SERS signals, but also can trap the target molecules into hot area, therefore, it can act as SERS-active platform for sensitive and credible detection of analytes.
Keywords/Search Tags:Dynamic Surface-enhanced Raman Spectroscopy, Raman probe, Surface-enhanced resonance Raman Spectroscopy, in situ detection, single hot site active substrate
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